Glow discharge switch



Aug. 24, 1943.

K. RATH GLOW DI SCHARGE SWITCH Filed June 19, 1942 2 Sheets-Sheet l INVENTOR.

Aug. 24, 1943. K. RATH GLOW DISCHARGE SWITCH Filed June 19, 1942 2 Sheets-Sheet 2 INVENT OR. u/ /ft Patented Aug. 24, 1943 l GLOW DISCHARGE SWITCH Karl Rath, New York, N. Y., assignor to Radio Patents Corporation, New York, N. Y., a corporation of New York lApplication June 19, 1942, Serial No. 447,643

` (c1. 20o-11s) 5 Claims.

My invention relates to glow discharge switches of the general type employing a bimetallic element to make and break the switch contacts, wherein the heat for actuating the bimetallic elements is generated by a .glow discharge in an ionizable gaseous medium. Such thermal switches are particularly useful for, though not limited thereto, the starting and operating of electric discharge devices, such as, for instance, fluorescent lamps of the well known type at present in commercial use.

Once the arc discharge is started, electric discharge devices such as the aforementioned flu-` orescent lamps which employ a pair of thermionic electrodes can be operated from a supply source having a standard operating voltage such as the usual house lighting or power circuits. Since the lamps have a negative voltageampere characteristic, they must be operated in series with an impedance preferably an inductance or choke coil to stabilize and limit the now of current to the designed value of the lamp, said inductance also servingv as a means for starting the discharge through the lamp. A voltage considerably higher vthan the supply voltage is necessary to start the discharge and it is advantageous not to start the discharge until after the lamp electrodes have been heated to the temperature at which they emit the necessary supply of electrons for reasons well known in the art.

For the above purpose it is customary to interconnect the two electrodes in series across the line by means of a glow discharge switch of the type referred to above. After the thermionic electrodes'of-the discharge device have been preheated to discharge 'sustaining temperature, the glow switch automatically breaks the connection, thereby subjecting the lamp to a transient voltage suiilcient to start a low voltage arc discharge. The Voltage drop across the lamp is not high enough to maintain the glow discharge through the switch so that the contacts will remain open as long as the lamp is in operation.

.Glow dischargeswitches for the above and Isimilar applications usually are desired to fulfill,

electrical conductance of the glow or arc path reestablished between the contacts at the instant of their separation and produced by the line and transient voltages should have a suiiiciently low value to produce a transient voltage across the lamp electrodes connected in shunt to the switch contacts sufficient to insure a safe and reliable starting of the low Voltage arc through the lamp or other discharge device.

Accordingly, among the general objects of myl invention are to provide an improved glow discharge switch which is both simple in design and of small size; which has a greatly reduced heating period or efficiency in heating the bimetallic v part discussed and in part become apparent as the following detailed description proceeds taken with reference to the accompanying drawings forming part of this specication and wherein:

Figure 1 is a vertical cross-sectional View shown partly in elevation of a glow discharge switch embodying the principles of my invention; Figure 2 is a horizontal sectiontaken on line 2-2 of Figure l; Figures 3 and 4 are views similar to Figure 1 illustrating modifications of the invention; Figure 5 is a vertical elevation, partly in Y section, of a further modification of a glow switch constructed in accordance with the invention; Figure 6 is a horizontal cross-section taken on line 1--1 of Figure 5; and Figure 7 is a diagrammatic illustration of a circuit for starting a low volta-ge arc discharge device having thermionic electrodes by means cf a glow switch according to the invention.

Like reference characters identify like parts in the different views of the drawings.

With the aforementionedobjects in view, the novel glow switch according to my invention in general comprises a pair of electrodes arranged in an ionizable medium, each of said electrodes having a heating portion of ,relatively large surface area and a separate switch or contact portion of relatively small 'surface area extending from said heating portions. Said heating portions, at least one of which is constituted of bior multi-metal sheet to cause a mechanical displacement thereof by varying temperature, are

arranged so as to present to each other a relatively large surface at close spacing to cause an intense glow discharge therebetween and to conine or concentrate the heat produced thereby as much as possible in the discharge space enclosed by the electrodes. This heat concentration has the effect of a quick heating of the bimetal element and rapid starting of the arc discharge device. The switch portions of said electrodes which may be in the form of wire elements or rods of the same or different metal (preferably tungsten) extend to a point remote from the discharge space and terminate in a pair of cooperating switch contacts designed to have the desired characteristics such as low electric conductance at the instant of separation of the contacts, substantially independently of the design and operation of the glow discharge electrodes.

Referring more particularly to Figures 1 and 2 of the drawings, the numeral I indicates a. preferably tubular insulating vessel or container of glass or the like'flled with a suitable ionizable gaseous medium such as argon, neon, mercury, etc., at low pressure or a mixture of such gases, and containing the electrodes and switching elements. The tube I0 has'a stem or press II and may be provided in a known manner with a metal base I2 shown of the screw-in type cemented or otherwise connected to the vessel I0 and serving as one oi the switch terminals, the remaining terminal being constituted by the central electrode element I3 insulatinglymounted upon the bottom of base I2. Item I4 represents the discharge portion of one of the electrode elements taking, in the example shown, the form of a metal plate or disc mounted concentrically to the container I0 and supported by a pair of rods or wires I5 and I6 welded or otherwise connected to diametrical points to said disc and sealed in the stem H. Supporting rod I5 extends through the stem and is electrically connected to one of the terminals I2 and I3. Item II` indicates a strip of suitable bimetallic metal sheet wound in spiral. form and disposed at a close distance and equally spaced from the disc electrode I4. The bimetallic element is supported by a rod having an upper flattened portion 2l welded or otherwisemechanically and electrically secured to the inner end thereof as shown more clearly in Figure 2. Supporting rod 20 passes through the center of stem II and is electrically connected to the remaining terminal of the switch. The outer end of the bimetallic spiral I1 is bent transversely as shown at 22 to provide a suitable contact surface cooperating with rod I6 extending from disc Id which serves as the cooperating contact of the switch. If desired, the metal base may be omitted and supporting rods I5 and 20 directly led to the outside in form of-tlexible wires for soldering or otherwise connecting to the parts of the circuit in which the switch is used.

In operation, the application of a suitable voltage which may be either of the direct current or alternating current type (in case of direct current, care should be taken that the vbirnetallic element forms the cathode or negative electrode) to the electrodes I2 and I3 will result in an electric glow discharge between disc I4 and spiral I1, said glow discharge being substantially equally distributed throughout the discharge space I8 therebetween, with the shortest possible current paths between the electrodes so as to result in an eiicient and duick heating of the bimetallic electrode by positive ion bombardment 4and rotation of the spiral and closing of the contacts I6 and r22. An advantage of the invention is due primarily to the employment of a pair of large surface electrodes disposed substantially parallel to or equidistantly from each other and at close Spacing so as to result in the shortest possible averager discharge path between one electrode to the other.` A further advantage resulting fr om the use of electrodes both of which have an extended surface area resides inthe fact, particularly in alternating current operation of the discharge devices, that the glow discharge will occur in either direction, thus utilizing both half waves of the alternating current cycle. Although in the case that the electrode I4 of Figure l con- Y stitutes'the cathode during one half cycle of the alternating current, the glow discharge will not directly heat the bimetallic element Il as efciently as during the half cycles when the element I'I is at negative potential, the glow discharge during the rst half cycles will contribute substantially in heating the bimetallic element by heat radiation and conduction through the gas due to the enclosed discharge space and shielding effect of the electrode I4 so as to result in a considerable decrease of the heating period required for closing the contacts I6 and 22.

It has been found advisable to coat the bi-V metallic element with an electrically active material in order to decrease the so-called cathode drop and to enable the switch to operate from standard potential sources at a voltage less than the line voltage and above the lamp voltage when the latter is in operation. For this purpose the birnetallic element is usually coated with electrically active material such as magnesium deposited thereon and upon the inner wall of the tube by evaporating a suitable supply introduced into the tube by means of an induction heating coil. According to the present invention the electrode I4 may be coated in a similar manner to improve -the operation when the latter acts as the cathode as described hereinbefore. The magnesium deposited on the glass walls and other parts within the tube acts ina known manner as a getter for absorbing undesirable occluded gases in the metal parts liberated during the operation of the device.

From the foregoing, it is seen that I have provided a glow discharge switch wherein the discharge electrodes proper, that is in the example v*of Figure 1 the bimetallic spiral I'I and the discshaped member I4 may be designed and arranged substantiallyindependently of the switch contact l elements 22 and I6, which latter form separate f 'extensions of said electrodes and are substantially independent of and in no way contribute 'to the glow -discharge for heating the bimetallic element. Accordingly the contact elements may be designed independently and consist of separate metal in such a manner as to insure most ecient operation in connection with the particular requirements and purpose for which the switch is designed.

In the case of starting an electric discharge device such as a iiuorescent lamp wherein the switch contacts are directly shunted across the lamp electrodes, and the lamp is started by a transient voltage produced at the instant of separation of the switch contacts, an important requirement is that the glow or arc discharge path the switch contacts at the instant of separation by the transient and line voltages should have a suiciently low conductance to insure an adequate striking voltage across the lamp electrodes sufficient to initiate a low voltage arc discharge. This object is easily accomplished by the design of the contact elements I6 and 22 independently of the remaining electrode portions, by choosing the -pro'per contact material such as tungsten and reducing both contact surfaces to an extent to obtain a suciently low conductance or a high impedance therebetween during the glow or initial arc formation at the instant of the. contact separation.

In the prior art itwas attempted to obtain a similar effect by using a large electrode in the form of a bimetallic element cooperating with an electrode having a comparatively small surface such as a rod or wire element. By making the surface of the latter as small as possible a low conductance at the interruption was to be obtained. Aside from the fact, as pointed out above, that such arrangement is greatly inferior with regard to quick heating and eflicient utilization of the heat produced by the glow discharge, lthe considerable inequality' of the contact sur- ,faces results in a low conductance in one direction of the current only, thereby utilizing only one of the half waves of the transient voltage and causing frequent failures or delays of the starting of the discharge through the lamp. By a construction according to the invention wherein both switch contacts may be of considerably reduced area, a low arc conductance is insured under all circumstances resulting in a more` efficient utilization of the transient voltage and safe and reliable starting of the discharge through the associate discharge device such as a fluorescent lamp.

Referring to Figure 3, I have shown a glow discharge switch similar to Figure 1 wherein for still better utilization and concentration of the glow discharge a second disc-shaped electrode I4 is disposed on the opposite side of the bimetallic spiral |1, said further electrode being also supported by the wires or rods |5 and I6 and provided with a, central opening for passing the supporting rod 26 of the spiral |1. There is also shown'in Figure 3 a metal base 24 of the bayonet type cemented to the discharge vessel l0 as shown at and'having a central Contact element |3 secured thereto by suitable insulating material 26.

The construction according to Figure 4 differs from the preceding embodiments by the provision of suitable insulating spacing elements such as a pair of discs 21 and 28 of mica or an equivlent substance frictionally or otherwise secured t the supporting rods |5, I6 and 20 to obtain an independent and self-supporting electrode assembly structure which may be pre-fabricated before being mounted in the tube I0.

Referring to Figures 5 and 6, I have shown another embodiment of a glow discharge switch embodying the principles of the invention. According to this modification one of the electrodes takes the form of a U-shaped bimetallic element 3|) while the other electrode 3| has the form of a plate arranged centrally and symmetrically to the electrode 30. The latter is supported by a rod 32 having a flattened end portion welded to the end of one leg of the U, while the former is has secured thereto an extension 35 terminating in a somewhat larger contact surface 31 opposite to and spaced from the contact 36. Electrode 3| may be of ordinary metal or of bior multi-metal sheet similar to the electrode 30, in which case the arrangement of the metal layers in the bimetallic elements should be such that increasing temperature will cause the free leg of electrode 30 to move in the direction opposite to the free end of electrode 3| as indicated by the arrows A and B, thereby further considerably decreasing the heating or operating period as is readily understood. Other advantages of this switch such as increased heat eliiciency and concentration to a restricted space as well as low electric conductance between the contacts 36 and 31 at the instant of separation, are substantially the same as described in connection with the preceding illustrations. Both electrodes may be coated with electronically active material and the tube filled with a suitable ionizable gaseous medium or mixture of gases at a suitable pressure in a. manner as will be obvious from the above. f

In Figure 1 there is shown diagrammatically a circuit preferably employed for starting and operating by means of a glow switch constructed in accordance with my invention an electric discharge device such as a well known fluorescent lamp now in commercial use. Said lamp as shown comprises in a known manner a glass tube 40 containing a suitable ionizable medium such as a mixture of inert gases and having its inner wall coated with a suitable fluorescent substance, at least one of said gases being capable of producing sumcient ultra-violet radiation for exciting said fluorescent substance. The ends of the tube are provided with suitable bases and terminal prongs 4|, 4|' and 42, 42 serving as terminals for the laments or thermionic electrodes 43 and 44, respectively, mounted at opposite ends within the tube.

Numeral 45 indicates a glow switch of the type according to the invention having a pair of electrodes each of which comprises a discharge portion 46 and 41 and switch contacts 43 and 49, respectively. Discharge portions 46 and 41, at least one of which consists of bimetal sheet and is supported to have its free contact `bearing end to move or become nexed under the influence of temperature changes, are spaced substantially equi-distantly to present a large discharge sur face at the shortest possible spacing, while the contacts 48 and 49 located at a point remote from the discharge space are designed to produce the most favorable transient Voltage therehf tween and across the lamp electrodes 43 and il in a manner described hereinabove.

The switch 45 is connected across one pair of opposite lamp terminals, in the example shown between the upper prongs 4| and 42 at the far side from lthe line terminals through suitable sockets .forming part of the lamp fixture while the line voltage of an ordinary alternating current light or power circuit is applied to the remaining terminals 4| and 42 in series with a choke coil 50 and a normal switch 5|.

In order to start the lamp, switch 5| is closed, thereby impressing the line voltage upon the electrodes 46 and 41 of the glow switch and initiating an abnormal glow discharge therebetween, resulting inthe heating of `the bimetal electrode 41 and closing of thecontacts 48 and 49. This in turn short-circuits the switch .and places the thermionic lamp electrodes 43 and 44 of the lamp in series across the line thereby heating the electrodes to electron emitting temperature suilicient to sustain a low voltage arc ing, and ernissive coating,

through the lamp. At the same time, the shortcircuiting of the glow switch results in a cessation of -e glow discharge and consequent cooling of the bimetal electrode 41 which in turn causes renewed opening of the contacts 48 and 49. At the instant of separation of the contact a high voltage surge or transient produced by the choke coil 5G momentarily causes a suciently high voltage across the pre-heated lamp electrodes 43 and M, resulting in the striking of a low`voltage arc which once started will be maintained by the line voltage with the electrodes 43 and 44 being maintained at discharge sustaining temperature by the discharge current through the lamp, Since the voltage drop through the lamp is substantially below the line voltage, a renewed operation of the glow switch 45 is prevented thus leaving the latter idle as long as the lamp is in operation. From this it follows that the switch should be designed, such as by employing the proper electrode material, a suitable gas and gas pressure, electrode spacetc., as to operate at a voltage below the line voltage and above the lamp voltage, which can easily be accomplished by the employment of the structure proposed by the invention.

' Items 52, 52 and 53, 53 are the usual shielding electrodes connected to the opposite ends of the filaments 43 and G, respectively, to prevent the electron current, emitted from one filament from entering th; other filament and to minimize positive ion bombardment and disintegration of the active surface coating of the filaments and therebyl prolonging the life of the lamps.

While I have shown and described in the foregoing several desirable embodiments 'of the invention, it is understood that this disclosure is for the purpose of illustration and that various changes in shape, proportion and arrangement of parts as well as the substitution of equivalent elements and materials for those herein shown and described may be made without departing from the spirit and scope of the invention as setforth in the appended claims.

I claim:

l. A glow discharge switch comprising a pair of electrodes at least one of which is a bi-metal elect' de, a container enclosing saidelectrodes, a rarified ionizable gaseous medium in said container, one of said electrodes being ,constituted by a plate bent into a U and the other electrode being a flat plate arranged symmetrically within the U, said bi-metal electrode being arranged to have one end thereof to move freely under the influence of an electric glow discharge betweenv said electrodes, and an electric contact carried by the free end of said bi-rnetal electrode.

2. A glow discharge switch comprising a pair of lbi-metal electrodes, a container enclosing -said electrodes, an ionizable gaseous medium in said container,- one of said electrodes substantially forming a U and the other electrode being arranged symmetrically within said U, both electrodes being arranged to have one end -thereof move freely in opposite directions under the inrluence of an electric glow discharge between the electrodes, and a pair of cooperating electric contact elements each are carried by one of the free ends of said electrodes.

3. A glow discharge switch comprising a container filled with an ionizable gaseous medium, al pair of bi-metallic large surface electrodes Within said container, one oi said electrodes substan, tially enclosing the other electrode at opposite sides thereof to provide a pair of large surface discharge spaces between said electrodes, botl,

said electrodes being arranged with one enc'f thereof adjacent to and moving freely towards each other under the influenceY of an electric glow discharge maintained therebetween, and a pair of cooperating electric contact elements each secured to one of the free ends of said electrodes.

4. A glow discharge switch comprising a oontainer filled with an ionizable gaseous medium,

a pair of bi-netallic electrode plates therein, oneA of said plates being bent into a U and the other plate being disposed symmetrically within said U to provide a pair of large surface discharge spaces between the opposite faces of said last mentioned plate and said U-shaped plate, both said plates being arranged with one end thereof adjacent to and moving freely towards each other under the iniiuence of an electric glow discharge maintained therebetween, and a pair of cooperating electric contact elements each secured to one of the free ends of said plates.

5. A glow discharge switch comprising acontainer filled with an ionizable gaseous medium, a pair of large surface electrodes within said container at least one of which consists of bimetal, one of said electrodes substantially enclosing the other electrode at opposite sides thereof to provide a pair of large surface discharge' spaces between said electrodes, said bimetal electrode being arranged to have one end thereof to move freely under theinuence often` electric glow discharge maintained between said electrodes, and an electric contact element secured to the free end of said bi-metallic elecv trede.

KARL RATH. 

